From the past, a magnetic tape apparatus using an open reel-type recording medium has been used for recording of data. However, in recent years, use is changed to a magnetic tape apparatus utilizing a cartridge-type recording medium, and an autochanger and/or a tape library apparatus in which the magnetic tape apparatus is incorporated and a plurality of cartridges is carried to the magnetic tape apparatus by a robot. Examples of the cartridge-type recording medium include Linear Tape-Open (LTO), Digital Linear Tape (DLT), and Digital Data Storage (DDS).
In connection with the open reel-type, it is known that the physical damage such as Z folding, edge folding, and the like occurs. However, the magnetic tape cartridge also suffers from edge damage of a tape which is caused due to a winding step generated when a magnetic tape is wound. In greater detail, the winding step is easily formed in the magnetic tape cartridge when a magnetic tape is wound around a reel flange because air is involved in winding. For such a reason, various means for suppressing occurrence of winding uneveness are attempted. For example, a fine gap is provided between the reel flange and the magnetic tape. However, if an impact is applied to the magnetic tape cartridge in the vertical direction, that is, in a width direction of the magnetic tape cartridge, the winding step is generated at arbitrary points of the magnetic tape. In addition, when a space layer between adjacent turns of the magnetic tape forcibly contracts due to the temperature and humidity influence, the winding step is generated.
Furthermore, the LTO is in its fourth generation and the recording capacity has doubled after each generation so far. For example, the first generation had a capacity of 100 GB and the fourth generation has a capacity of 800 GB. For realization of this, there is a tendency that the magnetic tape increases in length and decreases in thickness. That is, concomitantly with a recent increasing capacity, the magnetic tape of the magnetic tape cartridge has become longer and thinner. This also leads to more frequent occurrence of edge folding. The Z folding means the damage of the magnetic tape in which the magnetic tape is folded and bent in Z shape. The edge folding means the damage of the magnetic tape like in FIG. 14. That is, it means the type of damage in which the edge (end) of the magnetic tape is folded and the magnetic tape is creased at a portion of the magnetic tape that is staggeredly wrapped due to the winding and fastening force of the magnetic tape. FIG. 14 is a diagram for explaining the edge folding.
As a technique of detecting such physical damages, there has been known a magnetic tape apparatus employing a technique of performing a detection with the use of light which is reflected from the magnetic tape and a technique of performing a detection with the use of the roughness of the magnetic tape, for example, before data is written into the magnetic tape. There also have been known a technique of allowing a portion of the magnetic tape to be in an erased state so that writing is skipped at the portions where the physical damage is detected and a technique of writing a dummy block into such portions.
Examples of the related art include Japanese Laid-open Patent Publication No. 58-070445, Japanese Laid-open Patent Publication No. 02-058707, Japanese Laid-open Patent Publication No. 08-235672, and Japanese Laid-open Patent Publication No. 06-162626.
However, the related arts have a problem in that it is difficult to detect abnormality of a medium such as edge folding. In greater detail, the related art technology determines the presence or absence of the physical damage of the magnetic tape at a writing target point just at a timing in which data is being written in the magnetic tape. Accordingly, it is impossible to detect the edge folding which is a factor of the physical damage generated in the vertical direction, that is, in the width direction of the magnetic tape. As a result, in spite of the presence of the edge folding, in a case where the damage at the writing target point of the magnetic tape is shallow, writing of data continues and is completed. However, in a case where the occurred physical damage develops further thereafter, a retry operation is performed many times when the recorded data is read out, which causes a problem of a delay in data processing. Furthermore, there is a problem in that retries of reading end up in failure sometimes.